https://pfspipe.ipmu.jp/jira This file is an XML representation of an issue en-us 8.3.4 803005 13-09-2019 https://pfspipe.ipmu.jp/jira/browse/PIPE2D-685 DRP 2-D Pipeline <p>We try the median filter to get a whitened spectrum before spectral fitting. We have tried the spectral whitening method using Fourier transformation in <a href="https://pfspipe.ipmu.jp/jira/browse/PIPE2D-648" title="Spectral whitening of AMBRE templates and SDSS spectra" class="issue-link" data-issue-key="PIPE2D-648"><del>PIPE2D-648</del></a>. In this ticket, we study a detailed methodology of the median filter. We use AMBRE templates and observed SDSS stellar spectra for this study. </p> <p> </p> PIPE2D-685

Median filter to whiten an uncalibrated spectrum

Story Normal Done Done Takuji Yamashita Takuji Yamashita flux-cal-vector flux-calibration Tue, 15 Dec 2020 06:51:06 +0000 Fri, 28 Jan 2022 17:16:25 +0000 Mon, 15 Mar 2021 13:27:14 +0000 0 3 <p>I tried the median filter to the SDSS F-star spectra in Lee et al. 2011 and the AMBRE model templates. That works well in both samples. The broad Balmer lines and narrow other lines survive at the same time. Because the whitened spectra with the median filter look better than those with Fourier transformation, I would use the median filter as the first option.<br/>  <br/> The figures are the results of median filter whitening. Each panel follows one in the figures in <ins><a href="https://pfspipe.ipmu.jp/jira/browse/PIPE2D-648" title="Spectral whitening of AMBRE templates and SDSS spectra" class="issue-link" data-issue-key="PIPE2D-648"><del>PIPE2D-648</del></a></ins><ins>.</ins> The width of median filter is 72 pixels, which is comparable to 100 nm at 600 nm. Before applying the median filter, the lines and outliers are masked by sigma-clipping and the pixels around H alpha (645 nm &lt; λ &lt; 665 nm) are also masked. The blue part (&lt;~450 nm) is really worse due to many lines there.<br/>  <br/> Examples<br/> an SDSS spectrum (Teff~7000K):<br/> <span class="image-wrap" style=""><a id="13247_thumb" href="https://pfspipe.ipmu.jp/jira/secure/attachment/13247/13247_medianFilter_AMBRE_s6000_g%2B1.0_m1.0_t02_z%2B1.00_a%2B0.40.AMBRE_Extp.fits.png" title="medianFilter_AMBRE_s6000_g+1.0_m1.0_t02_z+1.00_a+0.40.AMBRE_Extp.fits.png" file-preview-type="image" file-preview-id="13247" file-preview-title="medianFilter_AMBRE_s6000_g+1.0_m1.0_t02_z+1.00_a+0.40.AMBRE_Extp.fits.png"><img src="https://pfspipe.ipmu.jp/jira/secure/thumbnail/13246/_thumb_13246.png" style="border: 0px solid black" /></a></span><br/>  <br/> an AMBRE template (Teff~6000):<br/> <span class="image-wrap" style=""><a id="13309_thumb" href="https://pfspipe.ipmu.jp/jira/secure/attachment/13309/13309_medianFilter_SDSS_spec-2184-53534-0083.png" title="medianFilter_SDSS_spec-2184-53534-0083.png" file-preview-type="image" file-preview-id="13309" file-preview-title="medianFilter_SDSS_spec-2184-53534-0083.png"><img src="https://pfspipe.ipmu.jp/jira/secure/thumbnail/13247/_thumb_13247.png" style="border: 0px solid black" /></a></span><br/>  <br/>  <br/>  <br/>  <br/>  </p> <p>Low temperature stars have many absorption lines. These can affect the result of the median filter whitening. This was pointed out in the 2D DRP telecon.<br/>  <br/> The whitened spectra of two low-temperature stars (Teff = 5400K and 6000K) are shown. As pointed out, there are a lot of small absorption lines and due to this, median filters are underestimating continua. In this media filtering process, I do the sigma clipping around a pre-whitened spectrum, but these small absorption lines are not clipped.<br/> Another filter, e.g., a filter tracing the first quartile, may improve it.<br/>  <br/> Teff=5400K (SDSS star)<br/> <span class="image-wrap" style=""><a id="13309_thumb" href="https://pfspipe.ipmu.jp/jira/secure/attachment/13309/13309_medianFilter_SDSS_spec-2184-53534-0083.png" title="medianFilter_SDSS_spec-2184-53534-0083.png" file-preview-type="image" file-preview-id="13309" file-preview-title="medianFilter_SDSS_spec-2184-53534-0083.png"><img src="https://pfspipe.ipmu.jp/jira/secure/thumbnail/13310/_thumb_13310.png" style="border: 0px solid black" /></a></span><br/>  <br/> Teff=6000K (SDSS star)<br/> <span class="image-wrap" style=""><a id="13309_thumb" href="https://pfspipe.ipmu.jp/jira/secure/attachment/13309/13309_medianFilter_SDSS_spec-2184-53534-0083.png" title="medianFilter_SDSS_spec-2184-53534-0083.png" file-preview-type="image" file-preview-id="13309" file-preview-title="medianFilter_SDSS_spec-2184-53534-0083.png"><img src="https://pfspipe.ipmu.jp/jira/secure/thumbnail/13309/_thumb_13309.png" style="border: 0px solid black" /></a></span></p> <p>We can close this ticket because we have discussed about this in the telecon. After generating flux calibration vectors using these whitened spectra, we will revisit the whitening study to improve the accuracy. </p> Blocks PIPE2D-651 PIPE2D-647 Development Epic Link PIPE2D-303 Rank 0|02qpq3:r1d Reviewers hassan Sprint 2DDRP-2021 A